Kelp are large seaweeds (algae), belonging to the brown algae and classified in the order Laminariales. There are about 30 different genera. Some species grow very long indeed, and form kelp forests.
Despite their plant-like appearance, some scientists group them not with the terrestrial plants (kingdom Plantae), but instead place them either in kingdom Protista or in kingdom Chromista.
Kelp grows in underwater "forests" (kelp forests) in clear, shallow oceans. It requires nutrient-rich water below about 20 °C (68 °F). It is known for its high growth rate — the genus Macrocystis and Nereocystis luetkeana grow as fast as half a metre a day, ultimately reaching 30 to 80 m.
Through the 19th century, the word "kelp" was closely associated with seaweeds that could be burned to obtain soda ash (primarily sodium carbonate). The seaweeds used included species from both the orders Laminariales and Fucales. The word "kelp" was also used directly to refer to these processed ashes.
In most kelp, the thallus (or body) consists of flat or leaf-like structures known as blades. Blades originate from elongated stem-like structures, the stipes. The holdfast, a root-like structure, anchors the kelp to the substrate of the ocean.
Gas-filled bladders (pneumatocysts
) form at the base of blades of American species, such as Nereocystis lueteana
(Mert.& Post & Rupr.) and keep the kelp blades close to the surface, holding up the leaves by the gas they contain.
Growth and reproduction
Growth occurs at the base of the meristem
, where the blades and stipe meet. Growth may be limited by grazing. Sea urchins
, for example, can reduce entire areas to urchin barrens
. The kelp life cycle involves a diploid sporophyte
and haploid gametophyte
stage. The haploid phase begins when the mature organism releases many spores, which then germinate to become male or female gametophytes. Sexual reproduction
then results in the beginning of the diploid sporophyte stage which will develop into a mature plant.
ash is rich in iodine
. In great amount, kelp ash can be used in soap
production. Until the Leblanc process
was commercialized in the early 1800s, burning of kelp in Scotland was one of the principal industrial sources of soda ash
(predominantly sodium carbonate
, a kelp-derived carbohydrate, is used to thicken products such as ice cream
, salad dressing
, and toothpaste
, as well as an ingredient in exotic dog food
and in manufactured goods. Giant kelp can be harvested fairly easily because of its surface canopy and growth habit of staying in deeper water.
Kelp is also used frequently in seaweed fertiliser, especially in the Channel Islands, where it is known as vraic.
Kombu (Laminaria japonica and others), several Pacific species of kelp, is a very important ingredient in Japanese cuisine. Kombu is used to flavor broths and stews (especially dashi), as a savory garnish (tororo konbu) for rice and other dishes, as a vegetable, and a primary ingredient in popular snacks (such as tsukudani). Transparent sheets of kelp (oboro konbu) are used as an edible decorative wrapping for rice and other foods.
Kombu can be used to soften beans during cooking, and to help convert indigestible sugars and thus reduce flatulence.
Because of its high concentration of iodine, brown kelp (Laminaria) has been used to treat goiter, an enlargement of the thyroid gland caused by a lack of iodine, since medieval times.
Kelp in history and culture
During the Highland Clearances
, many Scottish Highlanders
were moved off their crofts
, and went to industries such as fishing and kelping (producing soda ash
from the ashes of kelp). At least until the 1820s, when there were steep falls in the price of kelp, landlords wanted to create pools of cheap or virtually free labour, supplied by families subsisting in new crofting townships. Kelp collection and processing was a very profitable way of using this labour, and landlords petitioned successfully for legislation designed to stop emigration. But the economic collapse of the kelp industry in northern Scotland
led to further emigration, especially to North America
Natives of the Falkland Islands are sometimes nicknamed "Kelpers. The name is primarily applied by outsiders rather than the natives themselves.
See the article on seaweed fertiliser.
Overfishing nearshore ecosystems leads to the degradation of kelp forests. Herbivores are released from their usual population regulation, leading to over-grazing of kelp and other algae. This can quickly result in barren landscapes where only a small number of species can thrive.
Species of Laminaria in the British Isles
- Laminaria digitata (Hudson) J.V. Lamouroux (Oarweed; Tangle)
- Laminaria hyperborea (Gunnerus) Foslie (Curvie)
- Laminaria ochroleuca Bachelot de la Pylaie
- Laminaria saccharina (Linnaeus) J.V.Lamouroux (sea belt; sugar kelp; sugarwack)
Species of Laminaria world-wide
A comprehensive listing of species in Laminariales
and nearly all other algae orders is publicly accessible at http://www.algaebase.org.
- Laminaria agardhii (NE. America)
- Laminaria angustata (Japan)
- Laminaria bongardina Postels et Ruprecht (Bering Sea to California)
- Laminaria cuneifolia (NE. America)
- Laminaria dentigera Klellm. (California - America)
- Laminaria digitata (NE. America)
- Laminaria ephemera Setchell (Sitka, Alaska, to Monterey County, California - America)
- Laminaria farlowii Setchell (Santa Cruz, California, to Baja California - America)
- Laminaria groenlandica (NE. America)
- Laminaria japonica (Japan)
- Laminaria longicruris (NE. America)
- Laminaria nigripes (NE. America)
- Laminaria ontermedia (NE. America)
- Laminaria pallida Greville ex J. Agardh (South Africa)
- Laminaria platymeris (NE. America)
- Laminaria saccharina (Linnaeus) Lamouroux (Aleutian Islands, Alaska to southern California America)
- Laminaria setchellii Silva (Aleutian Islands, Alaska to Baja California America)
- Laminaria sinclairii (Harvey ex Hooker f. ex Harvey) Farlow, Anderson et Eaton (Hope Island, British Columbia to Los Angeles, California - America)
- Laminaria solidungula (NE. America)
- Laminaria stenophylla (NE. America)
Other genera in the Laminariales which may be considered as kelp
- Alaria marginata Post. & Rupr. (Alaska and California - America
- Costaria costata (C.Ag.) Saunders Japan; Alaska, California - America)
- Durvillea antarctica (New Zealand, South America, and Australia)
- Durvillea willana (New Zealand)
- Durvillaea potatorum (Labillardière) Areschoug (Tasmania; Australia)
- Ecklonia brevipes J. Agardh (Australia; New Zealand)
- Ecklonia maxima (Osbeck) Papenfuss (South Africa)
- Ecklonia radiata (C.Agardh) J. Agardh (Australia; Tasmania; New Zealand; South Africa)
- Eisena arborea Aresch. (Vancouver Island, British Columbia, Montrey, Santa Catalina Island, California - America)
- Egregia menziesii (Turn.) Aresch.
- ''Hedophyllum sessile (C.Ag.) Setch (Alaska, California - America)
- Macrocystis angustifolia Bory (Australia; Tasmania and South Africa)
- Pleurophycus gardneri Setch. & Saund. (Alaska, California - America)
- Pterygophora californica Rupr. (Vancouver Island, British Columbia to Bahia del Ropsario, Baja California and California - America)
Some animals are named after the kelp, either because they inhabit the same habitat
as kelp or because they feed on kelp. These include: